Hi estherowl, this is the place to ask questions like this. I am not sure what you are asking. Are asking about an MRes or should you do one?
MRes's can vary a lot and I would recommend you to do a lot of research into the individual courses. They can be a great stepping stone to a PhD or a waste of time. They can fill in gaps in your skill set and improve your chances of getting a PhD but there is no guarantee. If you had offers for both take the PhD in a heartbeat.
My other question is, are you committed to the project or do you mind doing something else? Because generally funding is won by the supervisor for a specific project. You can apply for your own funding for your idea but that is difficult (usually ). If you are flexible with PhD project it would be easier to get funding and you could better determine your knowledge/skills.
I hope that answered some questions